linux-phytec-ti

sphinx.rst: Allow Sphinx version 1.6 at the docs

Now that the PDF building issues with Sphinx 1.6 got fixed,
update the documentation and scripts accordingly.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>